Alkoxylated fatty acid alkyl esters belong to the class of non-ionic surfactants and are widely used for various applications.
While the well known addition of alkylene oxides onto fatty acids, i.e. compounds containing acidic hydrogen atoms, can be carried out in the presence of various, generally alkaline catalysts, the insertion of alkylene oxides into the ester bond of a fatty acid alkyl ester is far more difficult and can only be achieved using special catalysts.
There have been many attempts to obtain catalysts for alkoxylation of fatty acid alkyl esters that are both efficient as well as easy to prepare and use. Typically these compounds comprise alkaline earth metal compounds, in particular calcium and magnesium, in admixture with various cocatalysts. Representative examples include e.g. mixtures of at least two alkaline earth compounds and one or more additional materials selected from a carboxylic acid; a polyalkylene glycol, an C1-C10 alkyl-capped polyalkylene glycol and mixtures thereof together with at least one acid (WO 2006/025898). Other catalysts are based on mixtures of one or more alkaline earth metal salts of carboxylic and/or hydroxycarboxylic acids, an oxyacid, an alcohol and/or an ester, and a peroxy acid and/or a salt thereof (EP-A-2181763) or calcium salts of low molecular carboxylic and/or hydroxycarboxylic acids and/or hydrates of the former, in combination with a strong oxyacid, and an alcohol and/or an ester (WO 02/38269).
However, presently known methods of alkoxylating of fatty acid alkyl esters are still suffering from several disadvantages, in particular the need for external preparation of the catalyst (i.e. isolation of intermediates, etc.), the lack of a peaked homologue distribution, as well as unfavourable reaction conditions (e.g. high temperatures), etc. Thus, there is still a need for alkoxylation methods of fatty acid alkyl esters with both suitable and convenient reaction conditions as well as excellent reaction outcome (suitable for industrial scale).
Applicants have now found that a catalyst system based on either an alkaline earth metal oxide/mineral acid combination, in particular BaO/H2SO4, or a Lewis acid, in particular SuCl4, is able to overcome the problems associated with the prior art methods. In particular it was shown that the alkoxylation reaction of fatty acid alkyl esters results in alkoxylated products having a narrow oligomer distribution when an alkaline earth metal oxide/mineral acid combination, in particular BaO/H2SO4 combination, or to Lewis acid, in particular SnCl4, is used as a catalyst. Furthermore these methods can be performed in a one-pot reaction therefore eliminating the step of isolating any intermediate compounds, such as the external preparation of the catalyst and subsequent transfer into another reactor for the alkoxylation reaction according to the prior art.